Understanding when to use classes vs methods in OOP - switching frames with tkinter

Question

I'm trying to replicate an answer to my own accord from this answer/question here: Switch between two frames in tkinter

As you can see from the answer above, tehy instantiate multiple sub-classes of the Frame widget, and when we want to switch pages, we click a button and that class a method from our base class.

However, wouldn't creating multiple 'pages' methods under a 'Pages' class, be a lot cleaner and make sense? I'm not sure what to believe, and I would love clarification as to how I should be tackling this project, and why using classes or instanced methods would be better?

I've added my comments into the code below for lines I don't quite understand and I'm hoping I can gain some knowledge from the world of StackOverflow.

import Tkinter as tk

LARGE_FONT = ("Verdana", 12)

class Main(tk.Tk):

    def __init__(self, *args, **kwargs):
    ########### are we calling the Tk class from tkinter and passing in our 'Main' class?
        tk.Tk.__init__(self, *args, **kwargs)
    # why not self.container?
        container = tk.Frame(self)
    # again, should I be using self.page here instead?
        page = Pages(parent=container, controller=self)

        container.pack(side="top", fill="both", expand=True)

        container.grid_rowconfigure(0, weight=1)
        container.grid_columnconfigure(0, weight=1)

        self.frames = {}
        for F in ('page.page_one()', 'page.page_two()'):
        # what exactly does __name__ do? And how can I replicate this with my derived classes instanced methods?
            page_name = F#F.__name__
            frame = page#(parent=container, controller=self)
            self.frames[page_name] = frame
            frame.grid(row=0, column=0, sticky='nsew')

        self.show_frame("page.page_one()")

    def show_frame(self, page_name):
        frame = self.frames[page_name]
        frame.tkraise()

class Pages(tk.Frame):

    # i could just use *args, **kwargs here couldn't I?
    def __init__(self, parent, controller):
        tk.Frame.__init__(self, parent)
        self.controller = controller
        self.page_one(controller)

    # here I have my instance methods inside my derived 'Pages' class
    # isn't this much cleaner, having multiple instance methods inside a class?
    # or I should be separating each page into it's own instanced class?
    def page_one(self, controller):
        label = tk.Label(self, text='show_firmware_page', font=LARGE_FONT)
        label.pack(pady=10, padx=10)

        # how can I switch pages using the next button?
        next_btn = tk.Button(self, text='Next', command=lambda: controller.show_frame(self.page_two(controller)))
        quit_btn = tk.Button(self, text='Quit', command=lambda: controller.show_frame())

        quit_btn.pack()
        next_btn.pack()

    def page_two(self, controller):
        label = tk.Label(self, text='second_page', font=LARGE_FONT)
        label.pack(pady=10, padx=10)

        # how can I switch pages using the next button?
        next_btn = tk.Button(self, text='Next', command=lambda: Pages.show_frame("page_one"))
        quit_btn = tk.Button(self, text='Quit', command=lambda: Pages.show_frame())

        quit_btn.pack()
        next_btn.pack()


app = Main()
app.mainloop()

Basically, my current push is to try and use methods within my class in order to define my pages and switch between them. I'm currently having some trouble, and upon taking a look at other's answers, a lot of them have the idea that each class instantiates a Frame, in which we call a method to switch between those instances.

Let me know your thoughts on this process to get me up to speed about how I should be tackling this project.

Many thanks in advance for your help - I really want to get this OOP stuff down.

Answer 1

You could theoretically make methods in a single class reconfigure the UI the way you want, but it's probably not going to be easy.

Your current code can't work because there's no simple way for one of your methods to clean up the work done by another previous method (e.g. by getting rid of the label and buttons it created).

The original answer you linked to avoided that issue by having all the widgets created at the start of the program (not only when they're about to be displayed). Only one page is displayed at a time though, since they're all Frames that have been configured to display in the same location. The Frame that is on top hides the others and prevents their widgets from doing anything. By moving a different frame on top, you can switch between the pages.

If we ignore those widget display issues, you could make your main class call the methods you've written:

class Main(tk.Tk):

    def __init__(self, *args, **kwargs):
        container = tk.Frame(self) # I'm not sure a separate container is necessary
        container.pack(side="top", fill="both", expand=True)  # since we're only putting 
        container.grid_rowconfigure(0, weight=1)              # one other frame inside it
        container.grid_columnconfigure(0, weight=1)

        page = Pages(parent=container, controller=self)
        page.grid(row=0, column=0, sticky='nsew') # moved up from below

        self.frames = {}
        for F in (page.page_one, page.page_two): # no quotes or parentheses
            page_name = F.__name__ # the names are the strings "page_one" and "page_two"
            self.frames[page_name] = F

        self.show_frame("page_one")

    def show_frame(self, page_name):
        method = self.frames[page_name]
        method() # call the method we are switching to

class Pages(tk.Frame):
    def __init__(self, parent, controller):
        tk.Frame.__init__(self, parent)
        self.controller = controller

    def page_one(self):
        # do something to clean up previous pages here?
        label = tk.Label(self, text='show_firmware_page', font=LARGE_FONT)
        label.pack(pady=10, padx=10)

        next_btn = tk.Button(self, text='Next',
                             command=lambda: self.controller.show_frame("page_two")
        next_btn.pack()

    def page_two(self):
        label = tk.Label(self, text='second_page', font=LARGE_FONT)
        label.pack(pady=10, padx=10)

        next_btn = tk.Button(self, text='Next',
                             command=lambda: self.controller.show_frame("page_one"))
        next_btn.pack()

This will work (for some definition of "work"). I removed the quit buttons because I'm not sure exactly what the best way to handle them is (you probably don't want them to be calling show_frame).

Note that I'm by no means an expert at TKinter, so it's entirely possible that there's some easy way to remove the widgets from the previous page when you've moved on to the next one. I just don't know how.